The present invention relates to a method for separating materials in the form of particles and/or drops from a gas flow, in which method the gas flow is directed through a collection chamber, the outer walls of which are grounded; and in which method high tension is applied to ion yield tips arranged in the collection chamber so that an ion beam separating the desired materials from the gas flow is achieved towards the walls working as collection surfaces. The invention also relates to a device for applying the said method.
At present, filters, cyclones or electrical methods, such as electric filters or an ion blow or beam method, are used in gas purification systems and for separating particles from a gas flow.
When using filters, speed of the flowing gas has to be kept low in fabric or metal filters, because increasing the speed generates a strong air resistance. Also the resolution of the filters decreases along with the increase in speed. For example with micro filters, the gas flow speed is principally smaller than 0.5 m/second. In addition, it is not possible to achieve good cleaning results with the known techniques, when particles of nanometric category are concerned (i.e. particles the diameter of which is from a nanometer to a few dozen nanometers).
The operation of the cyclones is based on the decrease in the gas flow speed so that heavy particles in the gas flow fall down into the collection organ. Cyclones are thus applicable for separating heavy particles, because these have a high falling speed.
In electric filters, the separation of particles from gas is carried out onto collection plates or to interior surfaces of pipes. The speed of the flowing gas in electric filters has to be generally under 1.0 m/second, manufacturers"" recommendations being about 0.3-0.5 m/second. The reason for a small gas flow speed is that a higher flow speed releases particles accumulated onto plates, causing the resolution to decrease considerably. The operation of electric filters is based on the electrostatic charge of particles. However, it is not possible to electrically charge particles in the nanometric category. In addition, all materials are not charged electrically, as for example stainless steel.
In electric filters, low gas flow speed has to be used also because of the cleaning stage of the collection plates. When cleaning the plates, a blow is directed to the plates, releasing the collected particle material. The intention is that only the smallest possible amount of particle material released from the plates during the purification stage would get back to the flowing gas. With a small gas flow speed it is possible to achieve tolerable particle passing throughs.
The known technique is next described referring to the enclosed drawings, in which
FIG. 1 shows the equipment used in the ion blow method according to the known technique; and
FIG. 2 shows a method of the known technique for purifying the gas with the ion blow method.
In FIG. 1, there is shown an equipment for purifying gas in accordance with the known technique. The equipment shown comprises an inlet 1 for the incoming gas to be purified, an outlet 2 for the purified gas, a voltage cable 3, an insulator 4, a grounded collection chamber 5, an energized fastening rod 6, comprising several ion yield tips 7, a vibrator arrangement 8, a recovery channel 9 for collected particles, and a voltage source 10.
In FIG. 1, for example, air coming into a building or air to be recycled is directed to the collection chamber 5 for purification. The air to be purified gets into the collection chamber 5 through the inlet 1, rises upwards and, after purification, leaves through the outlet 2. The purification is carried out by ionizing the gas with ion yield tips 7 arranged to the energized fastening rod 6 and connected to the voltage source 10 via the voltage cable 3, the voltage source 10 being able to apply positive or negative (as in the figure) high tension to the fastening rod 6.
In other words, an ion blow is directed to the gas either positive or negative, and the ions and charged particles as well as uncharged particles are carried to the collection surface 5 along with the ion blow. The ion producing tips 7 are directed towards the grounded collection chamber 5 acting as the collection surface for the particles. The collection chamber 5 is insulated from the energized parts 6, 7 by the insulator 4. A voltage of about 70-150 kV is fed to the ion yield tips 7, and the distance of these from the collection chamber 5 is arranged so as to generate a conical ion blow effect so that the charged and uncharged particles are carried to the wall of the collection chamber 5 and adhere to it due to the charge difference between the 0 charge of the wall of the collection chamber 5 and the charge of the ion blow. The distance between the ion yield tips and the collection wall 5 is typically 200-800 mm.
FIG. 1 further shows the vibrator arrangement 8 for purifying the collection chamber 5 by vibration. The vibrator arrangement is designed so that as the chamber is vibrated, the collected particles fall down and leave through the recovery channel 9. The collected substance can also be removed by rinsing with water.
The ion blow method is characterized by a corona effect achieved by high voltage so that the voltage intensity is increased so much that an ion blow effect is generated from the ion yield tips to the desired grounded structure. A number of ion yield tips to be calculated separately is needed for each gas separation application. The ion beam method has been described more closely, for example, in the patent publication EP-424 335.
A solution for purifying gas in a collection chamber with the help of an ion blow method according to the known technique has been presented in FIG. 2. The figure shows an outlet 2 for the purified gas, a grounded collection chamber 5 and an energized fastening rod 6, comprising several ion yield tips 7. In addition, the figure shows the ion blow 11, particle accruals 12, 13 and 14 in the collection chamber 5, and the gas flow 15. The solutions in FIGS. 1 and 2 are characterized by the position of the ion yield tips in rings 22, with the help of which the distance between the ion yield tips and the collection surface is made shorter.
Especially in industry, in which several kilogrammes of substance have to be separated from big gas flows in one second, the ion beam equipment is relatively large, specifically because of the high voltage used.
In several industrial lines, it is difficult to find the necessary space for the equipment in the ion blow method.
The object of the present invention is to provide a method and a device, with which materials in the form of particles and/or drops can be separated from the gas flow, and power demand may be radically decreased and the detaching methods for the particle material accumulated onto the collection plates may be improved.
In the method of the invention, impurities are separated from the gas flow by a push-pull method, which is characterized in that the electrically conductive collection surfaces are electrically insulated from the outer casings, and that high tension is applied to the conductive collection surfaces, the high tension having the opposite polarity to the high tension applied to the ion yield tips. Compared with the known ion blow method described above, the difference is that the method of the invention has an electric field between the ion yield tips and the walls of the collection chamber as additional power. When applying high tension to the conductive collection surfaces, an electric field is generated in front of the collection surface, urging ions and particles that are charged with the opposite polarity from the high tension applied to the conductive collection surface towards the collection surface. With the said push-pull method, a better separation is achieved so that ion yield tips do not need to be attached to the rings, but they may be attached directly to the fastening rod.
By using the method of the invention, the operating voltage decreases to ⅓-xc2xc in relation to the method of the known technique shown in FIG. 2. At the same time, costs for achieving the same amount of air and the same purity level decrease considerably, even to ⅓.
A further object of the invention is to provide a device for carrying out the method of the invention described above. It is characteristic of the device of the invention that the electrically conductive collection surfaces are electrically insulated from the outer casings, and that high tension is applied from the voltage source to the collection surfaces, the high tension having the opposite sign of direct voltage as the high tension applied to the ion yield tips. In an embodiment of the invention there is a void provided between the electrical insulation and the outer casing.